The present invention relates to a process and an arrangement for influencing the timing periods of an internal-combustion engine that has at least one intake valve and one exhaust valve used for a charge cycle, with the timing of the intake valve with respect to the exhaust valve being changeable by means of a shifting element controlled by an electronic control unit for at least one rotational shifting speed stored in the control unit.
From the German Patent Document DE 34 21 028, an arrangement is known for influencing the timing periods of an internal-combustion engine with two camshafts in such a manner that the first camshaft changes its rotating position relative to the second camshaft. Such an arrangement changes the crossover time of the intake valves with respect to the exhaust valves and can therefore influence the course of the torque, the exhaust emissions, the power and the idling characteristics of an internal-combustion engine.
Normally, the adjustment of the camshaft as a function of the engine load and the rotational speed of the engine takes place such that, at least at a fixed rotational shifting speed of the internal-combustion engine, a shifting element is actuated which turns the intake camshaft with respect to the exhaust camshaft in such a manner that a shifting takes place from a small to a large valve crossover or vice versa, as known, for example, from the journal Motortechnische Zeitschrift MTZ 50 (1989), No. 4, Page 142.
Irrespective of how the timing periods are influenced, for example, by means of the turning of camshafts or by means of the connecting or disconnecting of charge cycle control valves, and whether this influencing is implemented electrically, hydraulically, mechanically, etc., a specific time interval is required in order to exercise this influence. In the case of the typical hydraulically or electrohydraulically operating arrangements, the length of this time interval is a function of the oil temperature and the oil pressure, with the oil pressure in turn being a function of the rotational speed.
The rotational shifting speed is normally placed in the intersecting point of the torque curves pertaining to the different timing periods so that, when the course of the torque pertaining, for example, to an early timing period falls, shifting takes place to the more advantageous course of the torque which pertains to a later timing period.
In any case, during the time interval which is required for the influencing of the timing periods, a mismatching takes place between the rotational speed of the engine and the possible torque occurring in the form of a torque break since this torque is not reached before the end of the time interval. The mismatching becomes larger with more dynamic driving through this non-optimal rotational shifting speed.
An object of the present invention is to provide a process for influencing the timing periods of an internal-combustion engine which avoids the above-mentioned disadvantages and ensures an optimal course of the torque in all rotational speed ranges.
This and other objects are achieved by the present invention which provides a process for influencing the timing periods of an internal-combustion engine that has at least one intake valve and one exhaust valve used for a charge cycle, with the timing the intake valve with respect to the exhaust valve being changeable by means of a shifting element controlled by an electronic control unit for at least one rotational shifting speed stored in the control unit. The process includes the step of displacing the rotational shifting speed to the value of an optimal rotational shifting speed that results in an optimal torque. This displacing is performed as a function of the time variation of the rotational speed of the internal-combustion engine by a rotational differential speed stored in at least one characteristic diagram of the control unit.
The process according to embodiments of the present invention advantageously avoids the torque break which occurs as a result of the time interval required for the influencing of the timing periods in which, as a function of the dynamics by which the rotational speed of the engine rises, the rotational shifting speed is displaced by a rotational differential speed to a value of an optimal rotational shifting speed. The value of this rotational differential speed, which depends with respect to time from the increase of the rotational engine speed, is stored in a characteristic diagram of a control unit of the internal-combustion engine. Since the time interval required for the turning operation is essentially constant, in an embodiment of the process of the present invention, the optimal rotational shifting speed is displaced farther in front of the fixed rotational shifting speed as the rotational engine speed more dynamically rises. In the practical driving operation of a motor vehicle equipped with an internal-combustion engine operating according to this process, this means that, for high acceleration operations, particularly in low driving positions of the transmission, the influencing of the timing periods is initiated so early that only a very slight mismatching occurs between the torque curves for the different timing periods which is clearly smaller than the mismatching in the case of a purely statically fixed rotational shifting speed.
The amount by which the fixed rotational shifting speed is advanced is determined in a simple manner on a dynamic engine test bed and is subsequently stored in a characteristic diagram of the already existing conventional electronic control unit of the internal-combustion engine.
This characteristic diagram comprises at least one characteristic curve for the full-load operation when the internal-combustion engine is in a hot-running condition and one characteristic curve for the operation at a lower engine oil temperature.
For a further improvement of the process, several characteristic diagrams may be stored in a memory file in the control unit in order to assign optimal rotational differential speeds, for example, to each individual driving position of the transmission. Furthermore, groups of rotational shifting speeds may be assigned to each characteristic diagram in order to, for example, at a low rotational speed, shift from a low to a high valve crossover, and vice versa in the case of a higher rotational speed.
As a function of the position of a driving program switch to be actuated manually which may also affect the transmission, in a further development, a shifting speed, which is optimal for the respective selected driving program, may be selected from a list of rotational shifting speeds or groups of rotational shifting speeds stored in the control unit.
The process of the present invention is suitable for any type of internal-combustion engine whose charge cycle is controlled by intake and exhaust valves.
The present invention also relates to an arrangement for influencing the timing periods of an internal-combustion engine that has at least one intake valve and one exhaust valve used for a charge cycle, and comprises an electronic control unit having at least one rotational speed stored in the control unit and a shifting element controlled by the electronic control unit that changes the timing of the intake valve with respect to the exhaust valve for the at least one rotational shifting speed stored in the control unit. There are means for displacing the rotational shifting speed to the value of an optimal rotational shifting speed that results in an optimal torque. The means for displacing operates to displace the rotational shifting speed as a function of the time variation of the rotational speed of the internal-combustion engine by a rotational differential speed stored in at least one characteristic diagram of the control unit. There are camshafts assigned to the intake and exhaust valves of the internal-combustion engine, and the shifting element is arranged coaxially adjacent to one of the camshafts.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.